1. Field of the Invention
This invention relates to a magnetic recording and reproducing apparatus having a rotor drum with a plurality of rotary magnetic head mounted thereon and reproducing amplifiers which are arranged so that recording and reproducing signals can be amplified and switched on the rotor drum.
2. Description of the Prior Art
Recently, magnetic recording and reproducing apparatus have become small-sized, light, efficient and have had convenient functions such as special reproducing mode added, but are not satisfactory to the increasing users demands. The further improvement of the magnetic recording and reproducing apparatus would be difficult using conventional techniques. So, new techniques are expected. Regarding the rotor drum portion, it has become necessary to mount more rotary magnetic heads on the rotor drum for realizing various special reproduction modes, long and high quality recording/reproducing modes and the so-called "video insert" mode which rewrites recorded video signals.
Conventionally, a rotary transformer is used for signal transmission between the rotary magnetic heads and the stator circuits. The number of the transmitting channels of the rotary transformer must be equal to that of the rotary magnetic heads. Accordingly, if the number of the rotary magnetic heads increases, the size of rotary transformer is large and disturbances to the video signals occur because of cross-talk between adjacent channels. Furthermore, since reproduced signals from the rotary magnetic heads are required to be broad-band for obtaining a high efficiency, the reproducing amplifiers must be placed as closely as possible to the rotary magnetic heads for decreasing stray capacitance.
FIG. 1 shows an example of a conventional magnetic recording and reproducing apparatus. In FIG. 1, elements 1a-1d are rotary magnetic heads, element 9 is a magnetic recording medium such as a magnetic tape. The rotary magnetic heads 1a-1d are coupled to stator circuits through a rotary transformer 3. Elements 2a-2d are channels of the rotary transformer 3 and the broken line shows the group of channels 2a-2d of the rotary transformer 3. Each of the rotary magnetic heads 1a-1d is connected one of the channels 2a-2d of the rotary transformer 3 as shown FIG. 1, which means that the number of channels of the rotary transformer is equal to that of the rotary magnetic heads. The channels 2a-2d of the rotary transformer 3 are coupled to reproducing amplifiers 5a-5d through recording/reproducing mode switching circuits 4a-4d. The reproducing amplifiers 5a-5d are connected to a reproducing head selection circuit 6. The mode switching circuits 4a-4d are further connected to a recording head selection circuit 7 which is connected to a recording amplifier 8.
During the reproducing mode, the mode switching circuits 4a-4d select the reproducing mode by a recording/reproducing mode switching signal. The reproduced signals are transferred to the reproducing amplifiers 5a-5d. The amplified signals are transferred to the reproducing head selection circuit 6 which selects a reproducing magnetic head according to a head selection signal so as to obtain the desired reproduced signal.
During the recording mode, a recording signal amplified by the recording amplifier 8 is transferred to a recording magnetic head which is selected by the recording head selection circuit 7 through one of the mode switching circuits 4a-4d and one of the channels 2a-2d of the rotary transformer 3. The mode switching circuits 4a-4d prevent the recording signal from being transferred to the reproducing amplifiers 5a-5d.
As described above, only a plurality of rotary magnetic heads and one set of windings of the rotary transformer are mounted on the rotor drum, and all signals are processed by the circuits located at the stator side. By this configuration, however, the rotary transformer 3 is usually installed in the cylinder unit and the mode switching circuits 4a-4d and the reproducing amplifiers 5a-5d are installed on a printed circuit board on the stator side together with other circuit blocks. Since the rotary magnetic heads are distant from the printed circuit board, the connection wires between the rotary transformer and the circuits on the printed circuit board are shielded and the stray capacitance is approximately 40-80 pF. Accordingly, the frequency characteristics during the playback mode cannot be wide. In other words, such a conventional example as above is unsuitable for broadening the frequency band of the amplifiers.
Furthermore, the signal loss of the rotary transformer 3 degrades the S/N ratio of the reproduced signal.
Still furthermore, FIG. 1 shows an example using four rotary magnetic heads, but the number of rotary magnetic heads must be increased for the special reproducing mode and the long play-and-audio reproducing modes. Therefore, the number of channels of the rotary transformer will increase and accordingly the size thereof will increase. This means that the number of rotary magnetic heads which can be practically mounted on the rotor drum is limited.